I had an EP3 for about two weeks. Loved it but returned it when the PL25 kept rattle-snaking. The EP3 has great AF, great ergonomics, and an excellent rear touch screen. The touch screen is the best I've used in any camera (iPhone type of touch screen) in terms of sensitivity. Much better than the rear LCD of the GH2, G3, GF2 and GF3. I briefly played with a GX1 today. The rear LCD seems to be the same as the other Panasonics in terms of resolution and touch capabilities. I like the ergonomic of the EP3 better. Build quality is about the same. I can't comment on performance or IQ of the GX1 because I really didn't use it enough.
You may want to ask this question at the MU-43 forum. I think a good number of folks there already have the GX1. Over here, I believe David (aka SoundImagePlus) may be the only one with actual experience with both cameras.